Move JoinString to the base namespace

ash/system/user/button_from_view.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/system/user/button_from_view.h"
 
 #include "ash/ash_constants.h"
 #include "ash/system/tray/tray_constants.h"
 #include "ash/system/tray/tray_utils.h"
 #include "base/strings/string_util.h"
@@ skipping 71 matching lines @@
   View::OnBlur();
   // Removing focus frame.
   SchedulePaint();
 }
 
 void ButtonFromView::GetAccessibleState(ui::AXViewState* state) {
   state->role = ui::AX_ROLE_BUTTON;
   std::vector<base::string16> labels;
   for (int i = 0; i < child_count(); ++i)
     GetAccessibleLabelFromDescendantViews(child_at(i), labels);
-  state->name = JoinString(labels, base::ASCIIToUTF16(" "));
+  state->name = base::JoinString(labels, base::ASCIIToUTF16(" "));
 }
 
 void ButtonFromView::ShowActive() {
   bool border_visible =
       (button_hovered_ && highlight_on_hover_) || show_border_;
   SkColor border_color = border_visible ? kBorderColor : SK_ColorTRANSPARENT;
   SetBorder(views::Border::CreateSolidBorder(1, border_color));
   if (highlight_on_hover_) {
     SkColor background_color =
         button_hovered_ ? kHoverBackgroundColor : kBackgroundColor;
     content_->set_background(
         views::Background::CreateSolidBackground(background_color));
     set_background(views::Background::CreateSolidBackground(background_color));
   }
   SchedulePaint();
 }
 
 }  // namespace tray
 }  // namespace ash